CN102912222B - 18MND5 low-alloy structural steel for nuclear power and technical control method for 18MND5 low-alloy structural steel - Google Patents

Abstract

The invention relates to the technical field of metallurgy, and aims to provide 18MND5 low-alloy structural steel for nuclear power and a technical control method for the 18MND5 low-alloy structural steel. The steel comprises, by mass, lower than or equal to 0.22% of C, from 0.10% to 0.30% of Si, lower than or equal to 0.012% of S, lower than or equal to 0.012% of P, lower than or equal to 1.5PPM (parts per million) of H, lower than or equal to 30PPM of O, from 1.15% to 1.60% of Mn, from 0.50% to 0.80% of Ni, from 0.43% to 0.57% of Mo, lower than or equal to 0.04% of Al, lower than or equal to 0.013% of N, lower than or equal to 0.25% of Cr, lower than or equal to 0.08% of Co, lower than or equal to 0.0018% of B, lower than or equal to 0.01% of V, lower than or equal to 0.08% of Cu, lower than or equal to 0.010% of As, lower than or equal to 0.002% of Sb, lower than or equal to 0.010% of Sn and the balance Fe. The mechanical performance of the 18MND5 material manufactured by the method is obviously superior to that of other types of steel, and the 18MND5 high-strength low-alloy structural steel can be used for pressure bearing for nuclear power.

Description

Structural low alloy steel and process control method for 18MND5 nuclear power

Technical field

The present invention relates to a kind of 18MND5 nuclear power pressure High-Strength Low-Alloy structure iron and process control method, belong to metallurgical technology field.

Background technology

Steel for nuclear power pressure equipment mainly refers to that the reactor housing, pressurized vessel, pressure pipeline etc. that are applicable to manufacture nuclear reactor support the material of reactor basic structure, must have the operation of protection nuclear power generating equipment simultaneously, prevent the effect of radioactive ray diffusion.Mainly adopt in the world Mn-Ni-Mo type Hi-Stren steel as core Steel Used for Pressure Retaining Components, be wherein most widely used with French 18MND5 type.At present in world wide, can produce this low alloy steel, be mainly France, Germany, the U.S., Russia and the advanced country such as Japanese.The domestic production for 18MND5 and research are relatively less, and not yet can accomplish scale production.Therefore; carry out early at home the research and development of 18MND5 pressure-bearing low-alloy structural steel ingot; have steel grades formula and the process control method of independent intellectual property right, form mass-producing, stable, mass production etc., be of great immediate significance and promotional value.

Summary of the invention

The technical problem to be solved in the present invention is, overcomes deficiency of the prior art, and a kind of 18MND5 nuclear power structural low alloy steel and process control method are provided.

The present invention, by improvement such as the formulation optimization to 18MND5 steel ingot chemical composition, smelting, hot-work, thermal treatments, proposes new 18MND5 material prescription and process control method.

This 18MND5 nuclear power by the chemical composition of structural low alloy steel is by mass percentage: C≤0.22%, Si 0.10～0.30%, S≤0.012%, P≤0.012%, H≤1.5PPM, O≤30PPM, Mn 1.15～1.60%, Ni 0.50～0.80%, Mo 0.43～0.57%, Al≤0.04%, N≤0.013%, Cr≤0.25%, Co≤0.08%, B≤0.0018, V≤0.01%, Cu≤0.08%, As≤0.010%, Sb≤0.002%, Sn≤0.010%, surplus is Fe.

The processing process controlling method of structural low alloy steel for this 8MND5 nuclear power, integrated control smelting burning forms steel ingot, forging steel ingot becomes forging and the thermal treatment to forging.

In the present invention, the processing condition that control smelting burning forms steel ingot are:

(1) selected starting material:

Select S≤0.020%; P≤0.020%; Other associated metal of the pure steel scrap of Co≤0.08%, the pure nickel plate of Co≤0.08% and high high-quality;

(2) at EAF(electric arc furnace) slightly refining:

Oxidation period: P takes off to≤0.004%, C and takes off to >=0.45%;

Reduction period: control slag (FeO) in 5% left and right, S takes off to≤0.005%, and other compositions reach specified requirement;

(3) at LF(refining furnace) refining:

Argon amount is controlled at 50～150L/min, treatment time >=30 minute; 1660 ℃～1680 ℃ of liquid steel temperature scopes;

(4) at VODC(vacuum oven) degassed:

Pumpdown time≤20min, suction < 1mbar; Control O≤30PPm, H≤1.5PPm;

Purify hot metal, reduces non-metallic inclusion to greatest extent;

(5) carry out ingot steel casting:

Adopt argon for protecting pouring; In mould, lead to argon gas 2～3 minutes, drive air in mould away and prevent secondary oxidation;

(6) carry out ingot annealing:

880 ℃ of heating and thermal insulations 8～12 hours; Stove is chilled to≤500 ℃ come out of the stove.

In the present invention, control forging steel ingot and become the processing condition of forging to be:

Heating temperature scope is 1180～1200 ℃, and forging all the time temperature range is 1150～800 ℃, total forging ratio >=3～4.

In the present invention, the process of thermal treatment condition of controlling forging is:

(1) forge postheat treatment: insulation at 850 ℃, soaking time 0.5～0.7 hour/inch, austenitizing; Stove is chilled to 350 ℃, every 100 millimeters of soaking times 0.8～1 hour, bainite; Be warming up to again 650 ℃, every 100 millimeters of soaking times 10～12 hours, perlite expands hydrogen; Heat rear stove to be chilled to≤150 ℃;

(2) conditioning heat treatment: 880 ℃ of heating and thermal insulations, soaking time 0.6～0.7 hour/inch, in still air hollow cold;

(3) property heat treatment: 880 ℃ of insulations water-cooled of coming out of the stove, soaking time 0.5～0.6 hour/inch; Air cooling after 640～660 ℃ of insulation tempering, soaking time 1～1.2 hour/inch.

Beneficial effect of the present invention is:

The mechanical property of the 18MND5 material of producing by method of the present invention is obviously better than other steel grades, can be used as nuclear power pressure 18MND5 High-Strength Low-Alloy structure iron.

Embodiment

(1) optimization of Chemical Composition

Because the 18MND5 the finished product of producing must meet French RCC-M standard, and controlling of production process method of the present invention is autonomous.So inventive improvements of invention, mainly on the basis of traditional 16Mn, 20MnMo, 16MnD, 20MnMoD material, by C from original 0.13～0.23% adjusting to≤0.22%, its objective is under the prerequisite that proof strength is suitable, increase the low-temperature flexibility of steel and reduce embrittlement transition temperature; Mn is adjusted into 1.15～1.6%% from original 1.1～1.6%, its objective is strengthening matrix, improves the hardening capacity of steel, reduces under built up welding clad crack susceptibility; Si is adjusted into 0.10～0.30% from original 0.17～0.60%, and its objective is and reduce the impact of radiation on steel, and the greying tendency of carbon in steel; Increase by≤0.25% Cr control examination, its objective is and improve the oxidation-resistance of steel and reduce the impact on steel heat resistance; Increase Ni0.50～0.80%, its objective is and improve the hardening capacity of steel and improve low-temperature flexibility; S from original≤0.015%, P≤0.20%, be strictly reduced to S, P all≤0.012%, its objective is and reduces its impact on steel prolongation property, toughness and welding property; Mo is adjusted into 0.43～0.57% from original 0.20～0.35%, its objective is and improves the thermotolerance of steel and reduce temper brittleness; Increase the examination to residual element: V≤0.010%; AL≤0.04%; H≤1.5PPm; O≤30PPm; Co≤0.080%; As≤0.010%; Sb≤0.002%; Sn≤0.010%; The examination of B≤0.0018%, its objective is that all many-sides such as reducing hot workability to steel, welding property, low-temperature performance have adverse influence.

18MND5 chemical composition (Wt/%) after optimization

(2) optimization of smelting technology condition

The processing process controlling method of High-Strength Low-Alloy structure iron for 18MND5 nuclear power: mainly comprise that burning forms steel ingot, forging steel ingot becomes the process such as forging and the thermal treatment to forging for smelting, obtain accurate process control parameter, and realized and controlling based on the integrated computer system of upper and lower computer.

Specifically be implemented as follows:

1, selected starting material

Select S≤0.020%; P≤0.020%; Other associated metal of the pure steel scrap of Co≤0.08%, the pure nickel plate of Co≤0.08% and high high-quality;

2, EAF(electric arc furnace) slightly refining

Oxidation period: P takes off to≤0.004%, C and takes off to >=0.45%;

Reduction period: control slag FeO in 5% left and right, S takes off to≤0.005%, and other compositions reach the composition requirement that table provides;

3, LF(refining furnace) refining

Submerged arc heating, Argon stirs should be abundant, is controlled at 50-150L/min by argon amount, and the treatment time should be >=and 30 minutes.By bottom Argon and electric-arc heating, make molten steel pool boiling, the impurity floating in molten steel forms slag blanket, thereby makes purification of molten steel, and the solubleness of oxygen, hydrogen reduces, and non-metallic inclusion is removed in desulfurization simultaneously and decarburization.The strict chemical composition of adjusting, adds for the available wire feeder of trace element of some shortcomings, improves the over-all properties of steel, guarantees to meet standard for acceptance.In LF stove, molten steel further heats up, for VODC stove creates conditions, and in the time that liquid steel temperature reaches 1660 ℃ ~ 1680 ℃, and meet the demands time tapping of composition.

4, VODC(vacuum oven) degassed

Pumpdown time≤20min, suction < 1mbar, detects the weight percentage of hydrogen in molten steel, oxygen in real time, guarantees O≤30PPm, H≤1.5PPm, purify hot metal, reduces non-metallic inclusion to greatest extent.

5, ingot steel casting

15-30 minute before cast inserts tunger tube in feed trumpet, in mould, leads to argon gas 2-3 minute, drives air in mould away and prevents secondary oxidation.In casting process, should adopt argon for protecting pouring, reduce the impact of outside air on molten steel.

6, ingot annealing

880 ℃ of heating and thermal insulations 8 ~ 12 hours, stove is chilled to≤500 ℃ come out of the stove, evenly ingot structure, and softening.

(3) forge

1180～1200 ℃ of Heating temperatures;

1150～800 ℃ of beginning final forging temperatures;

Total forging ratio >=3～4;

(4) forge postheat treatment

Insulation at 850 ℃, soaking time 0.5～0.7 hour/inch, austenitizing;

Stove is chilled to 350 ℃, every 100 millimeters of soaking times 0.8～1 hour, bainite;

Be warming up to again 650 ℃, every 100 millimeters of soaking times 10～12 hours, perlite expands hydrogen;

Heat rear stove to be chilled to≤150 ℃;

(5) conditioning heat treatment

880 ℃ of heating and thermal insulations, soaking time 0.6～0.7 hour/inch, in still air hollow cold;

(6) property heat treatment

880 ℃ of insulations water-cooled of coming out of the stove, soaking time 0.5～0.6 hour/inch;

Air cooling after 640～660 ℃ of insulation tempering, soaking time 1～1.2 hour/inch.

(3) test result

1, chemical composition detects and compares

2, mechanical property detects and compares

Can find out from test result, the mechanical property of the 18MND5 material of producing by method of the present invention is obviously better than other steel grades, can be used as nuclear power pressure 18MND5 High-Strength Low-Alloy structure iron.

3, the detection of surface quality

The surface of steel ingot exists without defects such as slag inclusion, pipe, crackle, overlaps.Defect can be removed with polishing process, the necessary rounding off of polishing defect, and the degree of depth, width, length ratio should be 1:5:8.Surface of steel ingot is without lobe, double teeming and serious subsurface porosity.

Finally, it is also to be noted that, what more than enumerate is only specific embodiments of the invention.Obviously, the invention is not restricted to above embodiment, can also have many technology destructing and deformation design.All distortion that those of ordinary skill in the art can directly derive or associate from content disclosed by the invention, all should think protection scope of the present invention.

Claims (3)

1. a processing process controlling method for structural low alloy steel for 18MND5 nuclear power, is characterized in that, integrated control smelting burning forms steel ingot, forging steel ingot becomes forging and the thermal treatment to forging;

The processing condition that described control smelting burning forms steel ingot are:

(1) selected starting material:

Select S≤0.020%; P≤0.020%; The pure steel scrap of Co≤0.08%, the pure nickel plate of Co≤0.08%, and other associated metal in the chemical composition of structural low alloy steel for described 18MND5 nuclear power;

(2) slightly refine at electric arc furnace:

Oxidation period: P takes off to≤0.004%, C and takes off to >=0.45%;

Reduction period: control slag FeO and take off to≤0.005% at 5%, S, other compositions reach the requirement of described composition;

(3) in the refining of LF refining furnace:

Argon amount is controlled at 50～150L/min, treatment time >=30 minute; 1660 ℃～1680 ℃ of liquid steel temperature scopes;

(4) degassed at VODC vacuum oven:

Pumpdown time≤20min, suction < 1mbar; Control O≤30ppm, H≤1.5ppm;

Purify hot metal, reduces non-metallic inclusion to greatest extent;

(5) carry out ingot steel casting:

Adopt argon for protecting pouring; In mould, lead to argon gas 2～3 minutes, drive air in mould away and prevent secondary oxidation;

(6) carry out ingot annealing:

880 ℃ of heating and thermal insulations 8～12 hours; Stove is chilled to≤500 ℃ come out of the stove;

The 18MND5 nuclear power structural low alloy steel preparing through preceding method, its chemical composition is by mass percentage: C≤0.22%, Si0.10～0.30%, S≤0.012%, P≤0.012%, H≤1.5ppm, O≤30ppm, Mn1.15～1.60%, Ni0.50～0.80%, Mo0.43～0.57%, Al≤0.04%, N≤0.013%, Cr≤0.25%, Co≤0.08%, B≤0.0018%, V≤0.01%, Cu≤0.08%, As≤0.010%, Sb≤0.002%, Sn≤0.010%, surplus is Fe.

2. method according to claim 1, is characterized in that, controls forging steel ingot and becomes the processing condition of forging to be: Heating temperature scope is 1180～1200 ℃, and forging all the time temperature range is 1150～800 ℃, and total forging ratio is 3～4.

3. method according to claim 1, is characterized in that, the process of thermal treatment condition of controlling forging is:

(1) forge postheat treatment: insulation at 850 ℃, soaking time 0.5～0.7 hour/inch, austenitizing; Stove is chilled to 350 ℃, every 100 millimeters of soaking times 0.8～1 hour, bainite; Be warming up to again 650 ℃, every 100 millimeters of soaking times 10～12 hours, perlite expands hydrogen; Heat rear stove to be chilled to≤150 ℃;

(2) conditioning heat treatment: 880 ℃ of heating and thermal insulations, soaking time 0.6～0.7 hour/inch, in still air hollow cold;

(3) property heat treatment: 880 ℃ of insulations water-cooled of coming out of the stove, soaking time 0.5～0.6 hour/inch; Air cooling after 640～660 ℃ of insulation tempering, soaking time 1～1.2 hour/inch.